In integrated circuit art, a commonly used method for forming interconnect structures, which include metal lines and vias, is known as “damascene.” Generally, this method involves forming an opening in a dielectric layer, which separates the vertically spaced metallization layers. The opening is typically formed using lithographic and etching techniques. After the formation, the opening is filled with copper or copper alloys. Excess copper on the surface of the dielectric layer is then removed by a chemical mechanical polish (CMP). The remaining copper or copper alloy forms vias and/or metal lines.
Copper is commonly used in damascene structures because of its low resistivity. Typically, an interconnect structure is formed of a plurality of metallization layers, each including a plurality of copper lines. Copper lines in different metallization layers are interconnected by vias. While copper is generally preferred due to its electrical characteristics, other materials may be used.